The Selkov model was analyzed by Dykman et
al. [1]} using eikonal methods, and the case
we consider here was chosen to reproduce the major qualitative
features seen in that analysis. Like the cross-catalytic CRN, the
Selkov CRN has a cubic mean-field equation and one linear steady-state
condition ensuring that all fixed points will lie along a line. It
generalizes the cross-catalytic CRN, in which the fixed-point line is
by construction the axis of symmetry under \(A \leftrightarrow B\) , to a
1-parameter degree of freedom setting the slope of the line. Unlike
the cross-catalytic CRN, where the slope is 1, in the Selkov model the
slope is negative. Thus the monotonicity of fixed-point values in
\(\left( {\bar{x}}_A , {\bar{x}}_B \right)\)  is opposite for species \(A\) 
and \(B\) , leading to a trade-off in the orders \(k_A\)  and \(k_B\)  along
the front where control of fluctuations switches from the more-stable
to the less-stable fixed point.
